For many prior art applications requiring large numbers of highly reliable switching operations, such as in the telephone industry, it was customary to use reed relays comprising a pair of contacts sealed in an inert gas atmosphere into a glass tube. For operation, the latter was inserted into the gap of an electromagnetic coil. These reed relays were expensive to fabricate, required ferro-nickel material for the reeds which has a coefficient of thermal expansion equal to that of glass into which the ends were heat sealed. In order to carry a limited current, the contact ends were formed of precious metal diffused into the iron. Furthermore, the glass envelope was fragile, so that great care was required in fabricating and using such relays. Moreover, the relay resulting from insertion of the reed into the coil was magnetically inefficient without provision for a magnetic return path.
In U.S. Pat. No. 4,788,516, having a common assignee with the present invention, there is disclosed a miniature electromagnetically actuated relay in which the movable armature and contacts are completely encapsulated within the central cavity of the bobbin on which the electromagnet is wound. The latter, which is of elongated rectangular section, with the corners rounded, is surrounded, end-for-end, by a U-shaped strap and heel piece, both of magnetic material, which provide a return path for the magnetic flux generated by current passing through the electromagnet. The common contact disposed to move in the cavity of the bobbin between a pair of fixed, normally-open and normally-closed contacts, comprises a precious metal double-face button supported by a beryllium-copper spring carrying a steel armature. The spring for the common contact has its fixed end anchored to the external end of the bobbin in internal welded contact with the U-shaped strap, which is integrally formed with an externally-depending terminal. The normally-open and normally-closed contacts are respectively supported by metal strips attached to opposite walls of the internal cavity of the bobbin, positioned to engage the armature contact to open or close, depending on whether the electromagnet is energized or not. The normally-open and normally-closed contacts are also connected to externally-depending terminals. A pair of power terminals are respectively connected to opposite ends of the electromagnet coil. Thus, the fixed and movable contacts are all completely enclosed within the cavity of the insulating bobbin on which the electromagnet coil is wound.
When voltage is applied to the coil, current flows through it, generating a magnetic flux flowing through the central cavity in the direction of the axis of the coil. The total flux is a function of the voltage applied, the current generated, and the reluctance of the magnetic circuit. In the magnetic circuit, the flux flows through the U-shaped strap, the magnetic armature attached to the common terminal, the contacting pole face, and the magnetic heel piece. The flux generated between the armature and the pole face generates a force which attracts the armature to the pole face, thus causing the normally-closed contact to open, and closing the normally-open contact.
The switch has the advantage that placing the contact and armature mechanism inside permits the coil volume to assume a larger proportion of the total volume of the relay, than is the case in conventional prior art designs, in which an external pole piece is used, and the contact assembly is outside of the coil.
It has been found, using the switch that for a given voltage input a lower current can generate the same force, and thus, a given power input to the coil will run cooler, dissipating more heat, enabling the operation of the relay to be more efficient.
Furthermore, the use of edge lay and inlay material in the normally-open and normally-closed contact element provides flat contacts which can be precisely located in the bobbin, resulting in minimal need for adjustment.
Furthermore, the construction of the switch is such that the armature and all movable parts, and the contacts, are inside of the coil and are thus protected against dust and foreign particles. When the relay of the present invention is used on a printed circuit board in conjuction with other electronic components which require the use of a conformal coating to protect the elements against moisture, this relay resists entry of the coating material into the area of the armature and contacts, thus eliminating the necessity for the relay to have an additional protective cover.
The volume is smaller, the coil is smaller, and the relay operates cooler than in the case of prior art relays operating to produce commensurate amounts of magnetic flux.
Further, because the relay is constructed so that the contacts and armature are protected, the relay may be readily handled with less chance of damages, or need for adjustment.
By lengthening the bobbin and its cavity in a direction transversal to the axis of the electromagnet, a plurality of sets of normally-open and normally-closed contacts may be enclosed, for servicing a series of electrical circuits, which may be connected or electrically isolated.
A particular feature of the relay is the inclusion, in the internal cavity of the electromagnet, of a small permanent magnet of one of the magnetic materials well-known today, such as an alloy of aluminum, nickel and cobalt, known by the trademark ALNICO, or a magnetic ceramic, or another of the well-known permanent magnetic materials. This is disposed across the cavity of the bobbin, between the normally-open and normally-closed contacts, and electrically isolated therefrom, if the magnet itself is not an insulator. This permanent magnet serves to augment or oppose the flux generated in the coil, depending on the direction of the electromagnet current and the orientation of the magnetic poles of the permanent magnet.
The aforementioned construction is substantially like that of U.S. Pat. No. 4,788,516 incorporated herein by reference.
It has been found that a slight change in pickup voltage may occur after performing the last step in the assembly process. This step in the assembly process consists of staking the base to the frame which may affect the reluctance in the magnetic circuit and that may, in turn, affect the pickup voltage. Inasmuch as the relay is enclosed, there is no access to the interior to make any adjustment.
Accordingly, among the objectives of the present invention are to provide a construction whereby the small enclosed relay can be readily adjusted without disassembly; and which construction does not adversely affect the operation of the relay; which is inexpensive.
In accordance with the invention, the magnetic armature is constructed and arranged such that it is accessible from the exterior of the enclosed relay to adjust the relay after it is assembled to conform with the desired level of voltage required to actuate the relay. Specifically, the magnetic armature is provided with an opening extending to the exterior of the housing such that a small tool, such as a pin, can be inserted to move the armature and apply force laterally to change slightly the angular relationship of the flexible contact which is fixed to the armature and thereby adjust the voltage, while observing the voltage on an electronic instrument.